2
Spatial Data Types and Metadata

The object-relational implementation of Oracle Spatial consists of a set of object data types, type methods, and operators, functions, and procedures that use these types. A geometry is stored as an object, in a single row, in a column of type SDO_GEOMETRY. Spatial index creation and maintenance is done using basic DDL (CREATE, ALTER, DROP) and DML (INSERT, UPDATE, DELETE) statements.

This chapter starts with a simple example that inserts, indexes, and queries spatial data. You may find it helpful to read this example quickly before you examine the detailed data type and metadata information later in the chapter.

2.1 Simple Example: Inserting, Indexing, and Querying Spatial Data

This section presents a simple example of creating a spatial table, inserting data, creating the spatial index, and performing spatial queries. It refers to concepts that were explained in Chapter 1 and that will be explained in other sections of this chapter.

The scenario is a soft drink manufacturer that has identified geographical areas of marketing interest for several products (colas). The colas could be those produced by the company or by its competitors, or some combination. Each area of interest could represent any user-defined criterion: for example, an area where that cola has the majority market share, or where the cola is under competitive pressure, or where the cola is believed to have significant growth potential. Each area could be a neighborhood in a city, or a part of a state, province, or country.

2.2 SDO_GEOMETRY Object Type

In the Spatial object-relational model, the geometric description of a spatial object is stored in a single row, in a single column of object type SDO_GEOMETRY in a user-defined table. Any table that has a column of type SDO_GEOMETRY must have another column, or set of columns, that defines a unique primary key for that table. Tables of this sort are sometimes referred to as geometry tables.

The sections that follow describe the semantics of each SDO_GEOMETRY attribute, and then describe some usage considerations (Section 2.2.6).

The SDO_GEOMETRY object type has methods that provide convenient access to some of the attributes. These methods are described in Chapter 9.

2.2.1 SDO_GTYPE

SDO_GTYPE indicates the type of the geometry. Valid geometry types correspond to those specified in the Geometry Object Model for the OGIS Simple Features for SQL specification (with the exception of Surfaces.) The numeric values differ from those given in the OGIS specification, but there is a direct correspondence between the names and semantics where applicable.

The SDO_GTYPE value is 4 digits in the format dltt, where:

d identifies the number of dimensions (2, 3, or 4)

l identifies the linear referencing measure dimension for a three-dimensional linear referencing system (LRS) geometry, that is, which dimension (3 or 4) contains the measure value. For a non-LRS geometry, or to accept the Spatial default of the last dimension as the measure for an LRS geometry, specify 0. For information about the linear referencing system (LRS), see Chapter 6.

tt identifies the geometry type (00 through 07, with 08 through 99 reserved for future use).

Geometry is a heterogeneous collection of elements.Foot 2 COLLECTION is a superset that includes all other types.

dl05

MULTIPOINT

Geometry has one or more points. (MULTIPOINT is a superset of POINT.)

dl06

MULTILINE or MULTICURVE

Geometry has one or more line strings. (MULTILINE and MULTICURVE are synonymous in this context, and each is a superset of both LINE and CURVE.)

dl07

MULTIPOLYGON

Geometry can have multiple, disjoint polygons (more than one exterior boundary). (MULTIPOLYGON is a superset of POLYGON.)

Footnote 1 For a polygon with holes, enter the exterior boundary first, followed by any interior boundaries.Footnote 2 Polygons in the collection can be disjoint.

The d in the Value column of Table 2-1 is the number of dimensions: 2, 3, or 4. For example, an SDO_GTYPE value of 2003 indicates a two-dimensional polygon.

Note:

The pre-release 8.1.6 format of a 1-digit SDO_GTYPE value is still supported. If a 1-digit value is used, however, Oracle Spatial determines the number of dimensions from the DIMINFO column of the metadata views described in Section 2.4.

Also, if 1-digit SDO_GTYPE values are converted to 4-digit values, any SDO_ETYPE values that end in 3 or 5 in the SDO_ELEM_INFO array (described in Section 2.2.4) must also be converted.

The number of dimensions reflects the number of ordinates used to represent each vertex (for example, X,Y for two-dimensional objects). Points and lines are considered two-dimensional objects. (However, see Section 6.2 for dimension information about LRS points.)

In any given layer (column), all geometries must have the same number of dimensions. For example, you cannot mix two-dimensional and three-dimensional data in the same layer.

The following methods are available for returning the individual dltt components of the SDO_GTYPE for a geometry object: GET_DIMS, GET_LRS_DIM, and GET_GTYPE. These methods are described in Chapter 9.

2.2.2 SDO_SRID

SDO_SRID can be used to identify a coordinate system (spatial reference system) to be associated with the geometry. If SDO_SRID is null, no coordinate system is associated with the geometry. If SDO_SRID is not null, it must contain a value from the SRID column of the MDSYS.CS_SRS table (described in Section 5.4.1), and this value must be inserted into the SRID column of the USER_SDO_GEOM_METADATA view (described in Section 2.4).

All geometries in a geometry column must have the same SDO_SRID value.

2.2.3 SDO_POINT

SDO_POINT is defined using the SDO_POINT_TYPE object type, which has the attributes X, Y, and Z, all of type NUMBER. (The SDO_POINT_TYPE definition is shown in Section 2.2.) If the SDO_ELEM_INFO and SDO_ORDINATES arrays are both null, and the SDO_POINT attribute is non-null, then the X and Y values are considered to be the coordinates for a point geometry. Otherwise, the SDO_POINT attribute is ignored by Spatial. You should store point geometries in the SDO_POINT attribute for optimal storage; and if you have only point geometries in a layer, it is strongly recommended that you store the point geometries in the SDO_POINT attribute.

Section 2.3.5 illustrates a point geometry and provides examples of inserting and querying point geometries.

Note:

Do not use the SDO_POINT attribute in defining a linear referencing system (LRS) point. For information about LRS, see Chapter 6.

2.2.4 SDO_ELEM_INFO

SDO_ELEM_INFO is defined using a varying length array of numbers. This attribute lets you know how to interpret the ordinates stored in the SDO_ORDINATES attribute (described in Section 2.2.5).

Each triplet set of numbers is interpreted as follows:

SDO_STARTING_OFFSET -- Indicates the offset within the SDO_ORDINATES array where the first ordinate for this element is stored. Offset values start at 1 and not at 0. Thus, the first ordinate for the first element will be at SDO_GEOMETRY.SDO_ORDINATES(1). If there is a second element, its first ordinate will be at SDO_GEOMETRY.SDO_ORDINATES(n), where n reflects the position within the SDO_ORDINATE_ARRAY definition (for example, 19 for the 19th number, as in Figure 2-3 later in this chapter).

SDO_ETYPE - Indicates the type of the element. Valid values are shown in Table 2-2.

SDO_ETYPE values 1, 2, 1003, and 2003 are considered simple elements. They are defined by a single triplet entry in the SDO_ELEM_INFO array. For SDO_ETYPE values 1003 and 2003, the first digit indicates exterior (1) or interior (2):

The use of 3 as an SDO_ETYPE value for polygon ring elements in a single geometry is discouraged. You should specify 3 only if you do not know if the simple polygon is exterior or interior, and you should then migrate the table or layer to the current format using the SDO_MIGRATE.TO_CURRENT procedure, described in Chapter 15.

You cannot mix 1-digit and 4-digit SDO_ETYPE values in a single geometry. If you use 4-digit SDO_ETYPE values, you must use 4-digit SDO_GTYPE values.

SDO_ETYPE values 4, 1005, and 2005 considered compound elements. They contain at least one header triplet with a series of triplet values that belong to the compound element. For SDO_ETYPE values 1005 and 2005, the first digit indicates exterior (1) or interior (2):

The use of 5 as an SDO_ETYPE value for polygon ring elements in a single geometry is discouraged. You should specify 5 only if you do not know if the compound polygon is exterior or interior, and you should then migrate the table or layer to the current format using the SDO_MIGRATE.TO_CURRENT procedure, described in Chapter 15.

You cannot mix 1-digit and 4-digit SDO_ETYPE values in a single geometry. If you use 4-digit SDO_ETYPE values, you must use 4-digit SDO_GTYPE values.

The elements of a compound element are contiguous. The last point of a subelement in a compound element is the first point of the next subelement. The point is not repeated.

SDO_INTERPRETATION - Means one of two things, depending on whether or not SDO_ETYPE is a compound element.

If SDO_ETYPE is a compound element (4, 1005, or 2005), this field specifies how many subsequent triplet values are part of the element.

If the SDO_ETYPE is not a compound element (1, 2, 1003, or 2003), the interpretation attribute determines how the sequence of ordinates for this element is interpreted. For example, a line string or polygon boundary may be made up of a sequence of connected straight line segments or circular arcs.

Descriptions of valid SDO_ETYPE and SDO_INTERPRETATION value pairs are given in Table 2-2.

If a geometry consists of more than one element, then the last ordinate for an element is always one less than the starting offset for the next element. The last element in the geometry is described by the ordinates from its starting offset to the end of the SDO_ORDINATES varying length array.

For compound elements (SDO_ETYPE values 4 and 5), a set of n triplets (one for each subelement) is used to describe the element. It is important to remember that subelements of a compound element are contiguous. The last point of a subelement is the first point of the next subelement. For subelements 1 through n-1, the end point of one subelement is the same as the starting point of the next subelement. The starting point for subelements 2...n-2 is the same as the end point of subelement 1...n-1. The last ordinate of subelement n is either the starting offset minus 1 of the next element in the geometry, or the last ordinate in the SDO_ORDINATES varying length array.

The current size of a varying length array can be determined by using the function varray_variable.Count in PL/SQL or OCIColSize in the Oracle Call Interface (OCI).

The semantics of each SDO_ETYPE element and the relationship between the SDO_ELEM_INFO and SDO_ORDINATES varying length arrays for each of these SDO_ETYPE elements are given in Table 2-2.

Table 2-2 Values and Semantics in SDO_ELEM_INFO

SDO_ETYPE

SDO_INTERPRETATION

Meaning

0

(any numeric value)

Type 0 (zero) element. Used to model geometry types not supported by Oracle Spatial. For more information, see Section 2.3.6.

1

1

Point type.

1

n > 1

Point cluster with n points.

2

1

Line string whose vertices are connected by straight line segments.

2

2

Line string made up of a connected sequence of circular arcs.

Each circular arc is described using three coordinates: the arc's start point, any point on the arc, and the arc's end point. The coordinates for a point designating the end of one arc and the start of the next arc are not repeated. For example, five coordinates are used to describe a line string made up of two connected circular arcs. Points 1, 2, and 3 define the first arc, and points 3, 4, and 5 define the second arc, where point 3 is only stored once.

1003 or 2003

1

Simple polygon whose vertices are connected by straight line segments. Note that you must specify a point for each vertex, and the last point specified must be identical to the first (to close the polygon). For example, for a 4-sided polygon, specify 5 points, with point 5 the same as point 1.

1003 or 2003

2

Polygon made up of a connected sequence of circular arcs that closes on itself. The end point of the last arc is the same as the start point of the first arc.

Each circular arc is described using three coordinates: the arc's start point, any point on the arc, and the arc's end point. The coordinates for a point designating the end of one arc and the start of the next arc are not repeated. For example, five coordinates are used to describe a polygon made up of two connected circular arcs. Points 1, 2, and 3 define the first arc, and points 3, 4, and 5 define the second arc. The coordinates for points 1 and 5 must be the same, and point 3 is not repeated.

1003 or 2003

3

Rectangle type (sometimes called optimized rectangle). A bounding rectangle such that only two points, the lower-left and the upper-right, are required to describe it.

Using this type (that is, defining a rectangle using only two points) is not supported for geodetic data; it is supported only for data associated with a Cartesian coordinate system. With geodetic data, define a rectangle using 5 points (with point 5 the same as point 1) and an SDO_INTERPRETATION value of 1. (You can also use the SDO_CS.VIEWPORT_TRANSFORM function to convert optimized rectangles to valid geodetic rectangles for use with the SDO_FILTER operator.)

1003 or 2003

4

Circle type. Described by three points, all on the circumference of the circle.

4

n > 1

Compound line string with some vertices connected by straight line segments and some by circular arcs. The value, n, in the Interpretation column specifies the number of contiguous subelements that make up the line string.

The next n triplets in the SDO_ELEM_INFO array describe each of these subelements. The subelements can only be of SDO_ETYPE 2. The last point of a subelement is the first point of the next subelement, and must not be repeated.

Compound polygon with some vertices connected by straight line segments and some by circular arcs. The value, n, in the Interpretation column specifies the number of contiguous subelements that make up the polygon.

The next n triplets in the SDO_ELEM_INFO array describe each of these subelements. The subelements can only be of SDO_ETYPE 2. The end point of a subelement is the start point of the next subelement, and it must not be repeated. The start and end points of the polygon must be the same.

2.2.5 SDO_ORDINATES

SDO_ORDINATES is defined using a varying length array (1048576) of NUMBER type that stores the coordinate values that make up the boundary of a spatial object. This array must always be used in conjunction with the SDO_ELEM_INFO varying length array. The values in the array are ordered by dimension. For example, a polygon whose boundary has four two-dimensional points is stored as {X1, Y1, X2, Y2, X3, Y3, X4, Y4, X1, Y1}. If the points are 3-dimensional, then they are stored as {X1, Y1, Z1, X2, Y2, Z2, X3, Y3, Z3, X4, Y4, Z4, X1, Y1, Z1}. Spatial index creation, operators, and functions ignore the Z values because this release of the product supports only two-dimensional spatial objects. The number of dimensions associated with each point is stored as metadata in the xxx_SDO_GEOM_METADATA views, described in Section 2.4.

The values in the SDO_ORDINATES array must all be valid and non-null. There are no special values used to delimit elements in a multielement geometry. The start and end points for the sequence describing a specific element are determined by the STARTING_OFFSET values for that element and the next element in the SDO_ELEM_INFO array as explained previously. The offset values start at 1. SDO_ORDINATES(1) is the first ordinate of the first point of the first element.

2.2.6 Usage Considerations

You should use the SDO_GTYPE values as shown in Table 2-1; however, Spatial does not check or enforce all geometry consistency constraints. Spatial does check the following:

For SDO_GTYPE values d001 and d005, any subelement not of SDO_ETYPE 1 is ignored.

For SDO_GTYPE values d002 and d006, any subelement not of SDO_ETYPE 2 or 4 is ignored.

For SDO_GTYPE values d003 and d007, any subelement not of SDO_ETYPE 3 or 5 is ignored. (This includes SDO_ETYPE variants 1003, 2003, 1005, and 2005, which are explained in Section 2.2.4).

The SDO_GEOM.VALIDATE_GEOMETRY function can be used to evaluate the consistency of a single geometry object or all the instances of SDO_GEOMETRY in a specified feature table.

The area (SDO_GEOM.SDO_AREA function) of the polygon is the area of the exterior polygon minus the area of the interior polygon. In this example, the area is 84 (99 - 15).

The perimeter (SDO_GEOM.SDO_LENGTH function) of the polygon is the perimeter of the exterior polygon plus the perimeter of the interior polygon. In this example, the perimeter is 52.9193065 (36.9193065 + 16).

An example of such a "polygon with a hole" might be a land mass (such as a country or an island) with a lake inside it. Of course, an actual land mass might have many such interior polygons: each one would require a triplet element in SDO_ELEM_INFO, plus the necessary ordinate specification.

Exterior and interior rings cannot be nested. For example, if a country has a lake and there is an island in the lake (and perhaps a lake on the island), a separate polygon must be defined for the island; the island cannot be defined as an interior polygon ring within the interior polygon ring of the lake.

In a multipolygon (polygon collection), rings must be grouped by polygon, and the first ring of each polygon must be the exterior ring. For example, consider a polygon collection that contains two polygons (A and B):

The elements in SDO_ELEM_INFO and SDO_ORDINATES must be in one of the following orders (depending on whether you specify Polygon A or Polygon B first):

A0, A1; B0, B1, B2

B0, B1, B2; A0, A1

2.3.3 Compound Line String

Figure 2-4 illustrates a crescent-shaped object represented as a compound line string made up of one straight line segment and one circular arc. Four points are required to represent this shape: points (10,10) and (10,14) describe the straight line segment, and points (10,14), (10,6), and (14,10) describe the circular arc.

The first triplet indicates that this element is a compound line string made up of two subelement line strings, which are described with the next two triplets.

The second triplet indicates that the line string is made up of straight line segments and that the ordinates for this line string start at offset 1. The end point of this line string is determined by the starting offset of the second line string, 3 in this instance.

The third triplet indicates that the second line string is made up of circular arcs with ordinates starting at offset 3. The end point of this line string is determined by the starting offset of the next element or the current length of the SDO_ORDINATES array, if this is the last element.

2.3.4 Compound Polygon

Figure 2-5 illustrates an ice cream cone-shaped object represented as a compound polygon made up of one straight line segment and one circular arc. Five points are required to represent this shape: points (6,10), (10,1), and (14,10) describe one acute angle-shaped line string, and points (14,10), (10,14), and (6,10) describe the circular arc. The starting point of the line string and the ending point of the circular arc are the same point (6,10). The SDO_ELEM_INFO array contains three triplets for this compound line string. These triplets are {(1,1005,2), (1,2,1), (5,2,2)}.

The first triplet indicates that this element is a compound polygon made up of two subelement line strings, which are described using the next two triplets.

The second triplet indicates that the first subelement line string is made up of straight line segments and that the ordinates for this line string start at offset 1. The end point of this line string is determined by the starting offset of the second line string, 5 in this instance. Because the vertices are 2-dimensional, the coordinates for the end point of the first line string are at ordinates 5 and 6.

The third triplet indicates that the second subelement line string is made up of a circular arc with ordinates starting at offset 5. The end point of this line string is determined by the starting offset of the next element or the current length of the SDO_ORDINATES array, if this is the last element.

You can search for point-only geometries based on the X, Y, and Z values in the SDO_POINT_TYPE specification. Example 2-7 is a query that asks for all points whose first coordinate (the X value) is 12, and it finds the point that was inserted in Example 2-6.

2.3.6 Type 0 (Zero) Element

Type 0 (zero) elements are used to model geometry types that are not supported by Oracle Spatial, such as curves and splines. A type 0 element has an SDO_ETYPE value of 0. (See Section 2.2.4 for information about the SDO_ETYPE.) Type 0 elements are not indexed by Oracle Spatial, and they are ignored by Spatial functions and procedures.

Geometries with type 0 elements must contain at least one nonzero element, that is, an element with an SDO_ETYPE value that is not 0. The nonzero element should be an approximation of the unsupported geometry, and therefore it must have both:

An SDO_ETYPE value associated with a geometry type supported by Spatial

An SDO_INTERPRETATION value that is valid for the SDO_ETYPE value (see Table 2-2)

(The SDO_INTERPRETATION value for the type 0 element can be any numeric value, and applications are responsible for determining the validity and significance of the value.)

The nonzero element is indexed by Spatial, and it will be returned by the spatial index.

The SDO_GTYPE value for a geometry containing a type 0 element must be set to the value for the geometry type of the nonzero element.

Figure 2-7 shows a geometry with two elements: a curve (unsupported geometry) and a rectangle (the nonzero element) that approximates the curve. The curve looks like the letter S, and the rectangle is represented by the dashed line.

The SDO_GTYPE value for the geometry is 2003 (for a two-dimensional polygon).

The SDO_ELEM_INFO array contains two triplets for this compound line string. For example, the triplets might be {(1,0,57), (11,1003,3)}. That is:

Ordinate Starting Offset
(SDO_STARTING_OFFSET)

Element Type
(SDO_ETYPE)

Interpretation
(SDO_INTERPRETATION)

1

0

57

11

1003

3

In this example:

The type 0 element has an SDO_ETYPE value of 0.

The nonzero element (rectangle) has an SDO_ETYPE value of 1003, indicating an exterior polygon ring.

The nonzero element has an SDO_STARTING_OFFSET value of 11 because ordinate x6 is the eleventh ordinate in the geometry.

The type 0 element has an SDO_INTERPRETATION value whose significance is application-specific. In this example, the SDO_INTERPRETATION value is 57.

The nonzero element has an SDO_INTERPRETATION value that is valid for the SDO_ETYPE of 1003. In this example, the SDO_INTERPRETATION value is 3, indicating a rectangle defined by two points (lower-left and upper-right).

Example 2-8 shows a SQL statement that inserts the geometry with a type 0 element (similar to the geometry illustrated in Figure 2-7) into the database. In the SDO_ORDINATE_ARRAY structure, the curve is defined by points (6,6), (12,6), (9,8), (6,10), and (12,10), and the rectangle is defined by points (6,4) and (12,12).

2.4 Geometry Metadata Structure

The geometry metadata describing the dimensions, lower and upper bounds, and tolerance in each dimension is stored in a global table owned by MDSYS (which users should never directly update). Each Spatial user has the following views available in the schema associated with that user:

USER_SDO_GEOM_METADATA contains metadata information for all spatial tables owned by the user (schema). This is the only view that you can update, and it is the one in which Spatial users must insert metadata related to spatial tables.

ALL_SDO_GEOM_METADATA contains metadata information for all spatial tables on which the user has SELECT permission.

DBA_SDO_GEOM_METADATA contains metadata information for all spatial tables on which the user has SELECT permission if the user has the DBA role.

Spatial users are responsible for populating these views. For each spatial column, you must insert an appropriate row into the USER_SDO_GEOM_METADATA view. Oracle Spatial ensures that the other two views (ALL_SDO_GEOM_METADATA and DBA_SDO_GEOM_METADATA) are also updated to reflect the rows that you insert into USER_SDO_GEOM_METADATA.

In addition, the ALL_SDO_GEOM_METADATA and DBA_SDO_GEOM_METADATA views have an OWNER column identifying the schema that owns the table specified in TABLE_NAME.

2.4.1 TABLE_NAME

The TABLE_NAME column contains the name of a feature table, such as COLA_MARKETS, that has a column of type SDO_GEOMETRY.

The table name is stored in the spatial metadata views in all uppercase characters.

The table name cannot contain spaces or mixed-case letters in a quoted string when inserted into the USER_SDO_GEOM_METADATA view, and it cannot be in a quoted string when used in a query (unless it is in all uppercase characters).

The spatial feature table cannot be an index-organized table if you plan to create a spatial index on the spatial column.

2.4.2 COLUMN_NAME

The COLUMN_NAME column contains the name of the column of type SDO_GEOMETRY. For the COLA_MARKETS table, this column is called SHAPE.

The column name is stored in the spatial metadata views in all uppercase characters.

The column name cannot contain spaces or mixed-case letters in a quoted string when inserted into the USER_SDO_GEOM_METADATA view, and it cannot be in a quoted string when used in a query (unless it is in all uppercase characters).

2.4.3 DIMINFO

The DIMINFO column is a varying length array of an object type, ordered by dimension, and has one entry for each dimension. The SDO_DIM_ARRAY type is defined as follows:

The SDO_DIM_ARRAY instance is of size n if there are n dimensions. That is, DIMINFO contains 2 SDO_DIM_ELEMENT instances for two-dimensional geometries, 3 instances for three-dimensional geometries, and 4 instances for four-dimensional geometries. Each SDO_DIM_ELEMENT instance in the array must have valid (not null) values for the SDO_LB, SDO_UB, and SDO_TOLERANCE attributes.

Note:

The number of dimensions reflected in the DIMINFO information must match the number of dimensions of each geometry object in the layer.

Spatial assumes that the varying length array is ordered by dimension. The DIMINFO varying length array must be ordered by dimension in the same way the ordinates for the points in SDO_ORDINATES varying length array are ordered. For example, if the SDO_ORDINATES varying length array contains {X1, Y1, ..., Xn, Yn}, then the first DIMINFO entry must define the X dimension and the second DIMINFO entry must define the Y dimension.

Example 2-1 in Section 2.1 shows the use of the SDO_GEOMETRY and SDO_DIM_ARRAY types. This example demonstrates how geometry objects (hypothetical market areas for colas) are represented, and how the COLA_MARKETS feature table and the USER_SDO_GEOM_METADATA view are populated with the data for those objects.

2.4.4 SRID

The SRID column should contain either of the following: the SRID value for the coordinate system (see Chapter 5) for all geometries in the column, or NULL if no specific coordinate system should be associated with the geometries.

2.5 Spatial Index-Related Structures

This section describes the structure of the tables containing the spatial index data and metadata. Concepts and usage notes for spatial indexing are explained in Section 1.7. The spatial index data and metadata are stored in tables that are created and maintained by the Spatial indexing routines. These tables are created in the schema of the owner of the feature (underlying) table that has a spatial index created on a column of type SDO_GEOMETRY.

2.5.1 Spatial Index Views

There are two sets of spatial index metadata views for each schema (user): xxx_SDO_INDEX_INFO and xxx_SDO_INDEX_METADATA, where xxx can be USER, DBA, or ALL. These views are read-only to users; they are created and maintained by the Spatial indexing routines.

2.5.1.1 xxx_SDO_INDEX_INFO Views

The following views contain basic information about spatial indexes:

USER_SDO_INDEX_INFO contains index information for all spatial tables owned by the user.

ALL_SDO_INDEX_INFO contains index information for all spatial tables on which the user has SELECT permission.

DBA_SDO_INDEX_INFO contains index information for all spatial tables on which the user has SELECT permission if the user has the DBA role.

The USER_SDO_INDEX_INFO, ALL_SDO_INDEX_INFO, and DBA_SDO_INDEX_INFO views contain the same columns, as shown Table 2-3, except that the USER_SDO_INDEX_INFO view does not contain the SDO_INDEX_OWNER column. (The columns are listed in their order in the view definition.)

Contains DEFERRED if the index status has been set to deferred (using the index_status keyword with the ALTER INDEX statement) and VALID if the index status is not deferred.

2.5.1.2 xxx_SDO_INDEX_METADATA Views

The following views contain detailed information about spatial index metadata:

USER_SDO_INDEX_METADATA contains index information for all spatial tables owned by the user. (USER_SDO_INDEX_METADATA is the same as SDO_INDEX_METADATA, which was the only metadata view for Oracle Spatial release 8.1.5.)

ALL_SDO_INDEX_METADATA contains index information for all spatial tables on which the user has SELECT permission.

DBA_SDO_INDEX_METADATA contains index information for all spatial tables on which the user has SELECT permission if the user has the DBA role.

Note:

These views were new for release 8.1.6. If you are migrating from an earlier release of Spatial, see Appendix A.

The USER_SDO_INDEX_METADATA, ALL_SDO_INDEX_METADATA, and DBA_SDO_INDEX_METADATA views contain the same columns, as shown Table 2-4. (The columns are listed in their order in the view definition.)

Contains TRUE if the index is geodetic (see Section 4.1.4) and FALSE if the index is not geodetic.

SDO_INDEX_STATUS

VARCHAR2

Contains DEFERRED if the index status has been set to deferred (using the index_status keyword with the ALTER INDEX statement) and VALID if the index status is not deferred.

2.5.2 Spatial Index Table Definition

The information in each quadtree spatial index table (each SDO_INDEX_TABLE entry as described in Table 2-4 in Section 2.5.1) depends on whether the index is an R-tree index or a quadtree index.

For an R-tree index, the spatial index table contains the columns shown in Table 2-5.

Table 2-5 Columns in an R-tree Spatial Index Data Table

Column Name

Data Type

Purpose

NODE_ID

NUMBER

Unique ID number for this node of the tree.

NODE_LEVEL

NUMBER

Level of the node in the tree. Leaf nodes (nodes whose entries point to data items in base table) are at level 1, their parent nodes are at level 2, and so on.

INFO

BLOB

Other information in a node. Includes an array of <child_mbr, child_rowid> pairs (maximum of fanout value, or number of children in each R-tree node, such pairs), where child_rowid is the rowid of a child node, or the rowid of a data item from the base table.

For a quadtree index, the spatial index table contains the columns shown in Table 2-6.

Table 2-6 Columns in a Quadtree Spatial Index Data Table

Column Name

Data Type

Purpose

SDO_CODE

RAW

Index entry for the object in the row identified by SDO_ROWID.

SDO_ROWID

ROWID

Rowid of a row in a feature table containing the indexed object.

SDO_STATUS

VARCHAR2

Contains I if the tile is inside the geometry, or contains B if the tile is on the boundary of the geometry.

SDO_GROUPCODE

RAW

Index entry at level SDO_LEVEL (hybrid indexes only).

For a quadtree index, the SDO_CODE, SDO_ROWID, and SDO_STATUS columns are always present. The SDO_GROUPCODE column is present only when the selected index type is HYBRID.

2.5.3 R-Tree Index Sequence Object

Each R-tree spatial index table has an associated sequence object (SDO_RTREE_SEQ_NAME in the USER_SDO_INDEX_METADATA view, described in Table 2-4 in Section 2.5.1). The sequence is used to ensure that simultaneous updates can be performed to the index by multiple concurrent users.

The sequence name is the index table name with the letter S replacing the letter T before the underscore (for example, the sequence object MDRS_5C01$ associated with the index table MDRT_5C01$).

2.6 Unit of Measurement Support

Geometry functions that involve measurement allow an optional unit parameter to specify the unit of measurement for a specified distance or area, if a georeferenced coordinate system (SDO_SRID value) is associated with the input geometry or geometries. The unit parameter is not valid for geometries with a null SDO_SRID value (that is, an orthogonal Cartesian system). For information about support for coordinate systems, see Chapter 5.

The default unit of measure is the one associated with the georeferenced coordinate system. The unit of measure for most coordinate systems is the meter, and in these cases the default unit for distances is meter and the default unit for areas is square meter. By using the unit parameter, however, you can have Spatial automatically convert and return results that are more meaningful to application users, for example, displaying the distance to a restaurant in miles.

The unit parameter must be enclosed in single quotation marks and contain the string unit= and a valid SDO_UNIT value from the MDSYS.SDO_DIST_UNITS or MDSYS.SDO_AREA_UNITS table. For example, 'unit=KM' in the following example (using data and definitions from Example 5-3 in Section 5.8) specifies kilometers as the unit of measurement:

Spatial uses the information in the MDSYS.SDO_DIST_UNITS and MDSYS.SDO_AREA_UNITS tables to determine which unit names are valid and what ratios to use in comparing or converting between different units.

The MDSYS.SDO_DIST_UNITS table contains the columns shown in Table 2-7.